Conjugated polymers continue to attract significant attention due to their desirable optical and electronic properties, which has led to their application in light emitting-diodes (LEDs), photovoltaic devices, sensors, electrochromic devices, and field effect transistors (FET). See (a) Semiconducting Polymers: Chemistry, Physics and Engineering; G. Hadziioannou and P. F. van Hutten, Eds.; Wiley-VCH: Weinheim, 2000; (b) Handbook of Oligo-and Polythiophenes, D. Fichou, Ed.; Wiley-VCH: Weinheim, 1999; and (c) J. Roncali, Chem. Rev. 1992, 92, 711.
The advantage of utilizing conjugated polymers in such applications is the ability to tune the properties of such materials at the molecular level. In particular, many of the properties of interest are dependent on the energetic width of the material's band gap (Eg), which is the energy between the filled valence and empty conduction bands and thus corresponds to the HOMO-LUMO gap of the solid state material. The Eg therefore determines both the lowest energy absorbance of the material and the energy of any potential emission. Low Eg values result in enhanced thermal population of the conduction band and increase the number of intrinsic charge carriers. In addition, the lower oxidation potential associated with low Eg values results in a stabilization of the corresponding doped (i.e., oxidized) state. See (a) J. Roncali, Chem. Rev. 1997, 97, 173; and (b) S. C. Rasmussen and M. Pomerantz, In the Handbook of Conducting Polymers, 3rd Ed.; T. A. Skotheim and J. R. Reynolds, Eds.; CRC Press: Boca Raton, Fla., 2007; Vol. 1, Chapter 12. Thus, control of the polymer band gap is an important factor in the production of technologically useful materials.
Currently there is a need for novel organic semi-conducting materials. Such materials will be useful, for example, in electrical devices, such as photovoltaic devices, sensors, display devices, and electrochromic devices, including components of plastic devices.